This invention relates to plenum type air distribution systems for head enclosures of the type worn during sandblasting operations, for example, and more particularly to a combination air diffusing and noise attenuating means for use in such systems.
Health and safety requirements dictate that those working in atmospheres contaminated with airborne substances wear a head enclosing hood the interior of which is supplied with pure respiration air. The respiration air is typically supplied under pressure to the interior volume of the hood through a tube having one or more openings within the hood. However, when a large volume of air under pressure passes through an opening, it will produce a whistle-like sound at an audible level that is particularly bothersome and fatiguing within a head enclosure or hood. Sounds tend to reverberate within an enclosure particularly where the enclosure is rigid and does not include means for damping or attenuating such sounds. Where the enclosure is a head enclosure, a very high noise level within the enclosure is easily achieved by a constant source of sound within the head enclosure.
It is an object of this invention to provide an improved plenum type air distribution system for use within a head enclosure which includes an air diffusion means that not only makes a reduced contribution to the sound present within the head enclosure, but also tends to attenuate sound within the enclosure.
It has been proposed in the prior art to reduce the contribution made by an air distribution system to the sound present within a head enclosure by increasing the number and decreasing the size of openings through which the air passes from the air supply tube to the interior of the head enclosure. This approach has been at least partially successful in that it has reduced the volume of the air flow through any particular opening in direct proportion to the number of such openings and inverse proportion to their size. However, it also has the tendency to merely raise the frequency of the sound above the audible range unless the openings are very small and numerous indeed. Sounds which are barely above the audible range can still produce harmful effects although the wearer of the helmet is not aware of such sounds.
It is a further object of this invention to provide an improved plenum-type air distribution system for use within a head enclosure in which the number of openings for the passage of air into the head enclosure is greatly increased and the size of such openings are reduced toward minimum to thereby reduce the amplitude and wavelengths of any sounds produced by such system toward minimum.
It is yet another object of this invention to provide an air distribution system of the type described which also includes means for attenuating sound within the head enclosure.
It is a still further object of this invention to provide an air distribution system of the type described having the above-mentioned advantages with little increase in the complexity and cost of the air distribution system.